use dashes in file names

manifest.json

@@ -18,7 +18,7 @@
                 "lib/browser-polyfill/custom-browser-polyfill.js",
                 "extension/index.js",
                 "extension/ui/content/infobar.js",
-                "lib/single-file/docHelper.js",
+                "lib/single-file/doc-helper.js",
                 "lib/single-file/frame-tree/content/frame-tree.js",
                 "extension/core/content/content-frame.js"
             ],